Technical Abstract:
Feed and manure nutrients pass through a continuous cycle on dairy farms. Cows are fed forages, grain, protein and mineral supplements to produce milk; land applied manure recycles nutrients through crops and pastures; and so on. The purpose of this chapter is to demonstrate how the types and amounts of forage, crude protein (CP) and mineral supplements fed to dairy cows impacts manure chemistry and the environmental outcomes of dairy production. An overview of potential environmental impacts of nutrient use is followed by an introduction of manure as a source of nutrients for crop production, including the relative availability of the nutrients contained in dairy manure components. The focus then changes to three main dietary ingredients, mineral P, forages and protein supplements, and their impacts on manure chemistry and environmental outcomes. Three examples of tradeoffs in feed and manure N management are then discussed including how reduction in dietary CP not only reduces ammonia emission from dairy barns and soil, but also the fertilizer N value of manure; the impacts of manure incorporation into soil on relative manure N loss via ammonia volatilization and nitrate leaching; and differences in manure N capture and cycling when cows deposit manure directly in the field (captures urine) versus in dairy barns (loss of ammonia). Some practices that enhance dietary impacts on manure chemistry and the environment are discussed, including tools such as the use of fecal P concentrations and milk urea N (MUN concentrations to monitor, evaluate, and balance levels of mineral P and CP in lactating dairy cow diets). Dairy nutrition consultants and veterinarians are critical partners in devising diets that maintain healthy, high producing dairy cows which produce manure that enhances environmental impacts of dairy farming systems.